A drill chuck as described in U.S. Pat. No. 5,765,839 has a body provided centered on an axis with an annular array of teeth and a plurality of jaws radially displaceable relative to the body between inner and outer positions. A tightening ring is axially fixed but rotatable about the axis on the body in a tightening direction and in an opposite loosening direction and a pair of screwthread formations between the tightening ring and the jaws move the jaws radially together on rotation of the tightening ring in the tightening direction and radially apart on rotation of the tightening ring in the loosening direction. A locking member engageable with the teeth and angularly fixed on the tightening ring is radially displaceable between a locking position engaging the teeth and preventing rotation of the body in the loosening direction and a freeing position permitting free rotation of the body relative to the tightening ring. A setting ring angularly displaceable on the tightening ring is formed with a pair of angularly spaced and radially open seats. A pair of angularly spaced abutments between the setting ring and the tightening ring limit angular movement of the sleeve on the ring. A cam on the setting ring is engageable with the locking member for displacing the locking member into the locking position when the setting ring is in one of its end positions and for displacing the locking member into the freeing position when the setting ring is in the other of its end positions.
With this system a tightening sleeve surrounds the chuck body, extending backward from the very front end. This sleeve is attached to the tightening ring so that the user gets a good grip on it to tighten or loosen the chuck. There is therefore no need for a separate key.
The disadvantage of this system is that, when drilling, the front end of the chuck often bumps up against the workpiece or another stationary object. Depending on the drilling direction, this engagement causes torque to be exerted on the tightening sleeve to loosen or tighten it. Thus the chuck can inadvertently be tightened so much that it is very difficult to loosen the chuck, or the chuck gets so loose the tool spins or falls out.